Titanium oxide and resin composition

ABSTRACT

Titanium oxide and a thermoplastic resin composition incorporated therewith, said titanium oxide being characterized by its property that it disperses into ethylene glycol (as a dispersing medium) to give a 13 wt % suspension which has a specific resistance higher than 7000 Ω·cm and passes through a filter paper with a pore size of 6 μm such that the filtration pressure does not exceed 100 kPa after filtration for 4 minutes at a flow rate of 1.73 cm 3  /min·cm 2 .

TECHNICAL FIELD

The present invention relates to titanium oxide and a process forproduction thereof and also to a thermoplastic resin compositioncontaining said titanium oxide.

BACKGROUND ART

Polyester consisting mainly of repeating units of ethylene terephthalatefinds use as fiber, film, moldings, etc. in a variety of industrialfields because of its outstanding moldability and physical properties.It is often incorporated with titanium oxide to impart whiteness,opacity, lubricity, etc. The resulting polyester resin composition,however, poses a problem with frequent filament breakage or filmbreakage during processing or with film defects leading to unevenprinting and surface irregularities.

Among several ideas proposed so far to address this problem is JapanesePatent Publication No. 265948/1988 which discloses a polyestercomposition containing highly dispersible titanium oxide characterizedby its specific average particle diameter and water content as well asits surface treatment with an aluminum compound and/or silicon compound.Unfortunately, the surface treatment contributes only a little toimprovement in the filament and film producing processes for its addedcost, because it has no effect on coarse particles originally present intitanium oxide.

DISCLOSURE OF THE INVENTION

The present inventors carried out extensive studies to radically reducecoarse particles originally present in titanium oxide by noting howtitanium oxide is dispersed in the resin composition. The studies led tothe present invention which covers:

1. Titanium oxide characterized by its property that it disperses intoethylene glycol (as a dispersing medium) to give a 13 wt % suspensionwhich has a specific resistance higher than 7000 Ω·cm and passes througha filter paper with a pore size of 6 μm such that the filtrationpressure does not exceed 100 kPa after filtration for 4 minutes at aflow rate of 1.73 cm³ /min·cm².

2. A thermoplastic resin composition which comprises a thermoplasticresin and the titanium oxide defined above.

3. A thermoplastic resin composition which comprises a polyester resinand the titanium oxide defined above.

4. A polyester resin composition which is composed of a polyester resinand titanium oxide and is characterized by its property that it passesthrough a filtration pressure tester under the following conditions suchthat the rise in filtration pressure after filtration for 1 hoursatisfies the equation (I) below.

    P≦0.2C+0.2                                          (I)

where P is the rise in filtration pressure (MPa) and C is the content(wt %) of titanium oxide in the composition, provided that 0.3≦C ≦15.

Measuring temperature: 300° C.

Rate of filtration: 1.11 g/min·cm²

Pore size of filter: 7 μm

5. A process for producing a polyester resin composition composed of apolyester resin and titanium oxide, said process comprising adding asuspension in ethylene glycol of the titanium oxide defined in (1) abovein the course of polymerization for polyester resin.

6. A process for producing a polyester resin composition composed of apolyester resin and titanium oxide, said process comprisingincorporating, by using a mixer, the titanium oxide defined in (1) aboveinto a polyester resin after the polymerization for the polyester resinis substantially complete.

7. A process for producing titanium oxide which comprises the steps ofdispersing raw titanium oxide into a liquid, clearing the resultingtitanium oxide dispersion of coarse titanium oxide particles, freeingthe titanium oxide dispersion of liquid by drying, and causing thetitanium oxide obtained in the previous step to impinge upon an objectby the aid of a gas stream.

8. A process as defined in (7) above which gives rise to titanium oxidecharacterized by its property that it disperses into ethylene glycol (asa dispersing medium) to give a 13 wt % suspension which has a specificresistance higher than 7000 Ω·cm and passes through a filter paper witha pore size of 6 μm such that the filtration pressure does not exceed100 kPa after filtration for 4 minutes at a flow rate of 1.73 cm³/min·cm².

BRIEF DESCRIPTIONS OF THE FIGURES

FIG. 1 is a schematic sectional view illustrating how to test thefiltering characteristics in the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is concerned with particulate titanium oxidecharacterized by its property that it disperses into ethylene glycol (asa dispersing medium) to give a 13 wt % suspension which has a specificresistance higher than 7000 Ω·cm and passes through a filter paper witha pore size of 6 μm such that the filtration pressure does not exceed100 kPa after filtration for 4 minutes at a flow rate of 1.73 cm³/min·cm². A failure to meet these requirements results in a polyesterresin composition which is subject to frequent filament breakage duringspinning. The filter paper with a pore size of 6 μm is available fromNippon Por Co., Ltd. under a trade name of "Ultipor GF" Discs P/N 6micron 47 mm.

The titanium oxide specified above may be prepared by the followingprocedure.

1. Dispersing raw titanium oxide into a liquid (such as water).

2. Removing coarse particles of titanium oxide by centrifuging or thelike.

3. Recovering titanium oxide particles from the dispersion byevaporation.

4. Causing titanium oxide particles to collide with each other or toimpinge upon an object (such as walls of the apparatus or baffles placedin the apparatus) by the aid of a gas jet stream, thereby crushingcoarse particles which might have occurred due to aggregation in step(3) above.

The titanium oxide of the present invention is intended to beincorporated into a thermoplastic resin, preferably a polyester resin,for production of a resin composition. The polyester is one in which thedicarboxylic acid moiety is terephthalic acid (or an ester-formingderivative thereof) and the glycol moiety is ethylene glycol or butyleneglycol (or an ester-forming derivative thereof). Preferred examplesinclude polyethylene terephthalate and polybutylene terephthalate. Otherexamples include copolyesters in which more than 70% of the repeatingunits in the main chain is ethylene terephthalate or tetramethyleneterephthalate, with the terephthalic acid moiety being partly replacedby a difunctional carboxylic acid (or an ester-forming derivativethereof) and the glycol moiety being partly replaced by an aliphatic,alicyclic, or aromatic dihydroxy compound (or an ester-formingderivative thereof). The difunctional carboxylic acid includes, forexample, sodium 5-sulfoisophthalic acid, potassium 5-sulfoisophthalicacid, p-β-hydroxyethoxybenzoic acid, p-hydroxybenzoic acid, isophthalicacid, 4,4'-diphenyletherdicarboxylic acid,4,4'-diphenylmethanedicarboxylic acid, 4,4'-diphenyletherdicarboxylicacid, 4,4'-diphenyldicarboxylic acid,1,2'-diphenoxyethane-p,p'-dicarboxylic acid, 2,6-naphthalenedicarboxylicacid, adipic acid, and sebacic acid. The dihydroxy compounds include,for example, trimethylene glycol, tetramethylene glycol, hexamethyleneglycol, diethylene glycol, triethylene glycol, polyethylene glycol,1,4-cyclohexanediol, 1,4-cyclohexanedimethanol,1,4-bis-β-hydroxyethoxybenzene, and bisphenol A.

The polyester resin may be produced continuously or batchwise.Production of polyethylene terephthalate (as a polyester resin) consistsof two steps. The first step involves the direct esterification reactionbetween terephthalic acid and ethylene glycol, or the ester interchangereaction between dimethyl terephthalate (as a lower alkyl ester ofterephthalic acid) and ethylene glycol, or the reaction betweenterephthalic acid and ethylene oxide which yields a glycol ester ofterephthalic acid and/or an oligomer thereof. The second step involvesthe polycondensation reaction under reduced pressure to produce apolymer with a desired degree of polymerization from the reactionproduct obtained in the first step.

In the process of producing the polyester resin composition of thepresent invention, it is possible to add titanium oxide in the course ofpolymerization of the polyester resin, or after the polymerization issubstantially complete, or after the polyester resin has been made intopellets, with the former two methods being preferable. A preferred wayfor the first method is to disperse titanium oxide into glycol and addthe resulting dispersion to the polymerization system containing anoligomer of polyester. A preferred way for the second method is toincorporate titanium oxide directly into molten polymer immediatelyafter polymerization using a mixer.

According to the present invention, the polyester resin compositioncomposed of a polyester resin and titanium oxide should meet therequirement that it passes through a filtration pressure tester suchthat the rise in filtration pressure after filtration for 1 hoursatisfies the equation (I) below.

    P≦0.2C+0.2                                          (I)

where P is the rise in filtration pressure (MPa) and C is the content(wt %) of titanium oxide in the composition, provided that 0.3≦C+15 whentested under the condition that the measuring temperature is 300° C.,the rate of filtration is 1.11 g/min·cm², and the pore size of thefilter is 7 μm.

The filter that can be used for this test is "Dynaloy Filter X5". Thefiltration pressure tester is available from Fuji Filter Kogyo Co.,Ltd., and the filter is available from Watanabe Giichi Seisakusho Co.,Ltd. (in Kyoto).

The filtration test is illustrated in FIG. 1. It consists of the stepsof:

1. charging a sample of polyester resin composition (in the form ofpellets) into the hopper 1.

2. heating the aluminum block heater 4 until the hot plate 3 is heatedto 300° C. (which is the measuring temperature).

3. actuating the piston 2, thereby pressing the melt of the sampleagainst the hot plate.

4. running the gear pump 5, thereby discharging the melt of the samplethrough the filter at a prescribed rate for 4 hours, and recording thefiltration pressure on the recorder 7 during discharging.

The polyester resin for incorporation with the titanium oxide of thepresent invention may be polymerized batchwise or continuously. In thesecond case, it is desirable to add titanium oxide after polymerizationis substantially complete. This obviates the necessity of purging thepolymerizer but it is only necessary to purge the mixer when one gradeof polyester resin composition is to be switched to another.

EXAMPLES

The invention will be described in more detail with reference to thefollowing examples.

Preparation of titanium oxide samples A to E:

Five samples A to E of titanium oxide for incorporation into polyesterresin were prepared by the process shown in Table 1 from raw titaniumoxide (TA-110) available from Fuji Titan Kogyo Co., Ltd.). The processinvolves the centrifugal separation of coarse particles and themechanical crushing of coarse particles. The former is accomplished byusing an ultracentrifuge ("Super-decanter P-3000" from Tomoe EngineeringCo., Ltd.). The latter is accomplished by using a dry crusher ("Jet MillSTJ-200" from Seishin Kigyo Co., Ltd.) which is designed such thatcoarse particles are caused to impinge upon the wall of the equipment bymeans of an air jet. The rates of crushing for samples D and E are 10kg/h and 5 kg/h, respectively.

Each of titanium oxide samples A to E was mixed with ethylene glycol togive a 13 wt % suspension. The suspension was stirred at 300 rpm for 1hour. Then the suspension was passed through a filter paper (47 mm indiameter, specified above) at a flow rate of 30 cm³ /min (which isequivalent to 1.73 cm³ /min·cm²) and the rise in filtration pressure wasmeasured. The specific resistance of the suspension was measured in thefollowing manner. A sample (20 g) is dispersed into pure water (180 g)by thorough mixing in a 300-ml beaker. This pure water should have aspecific resistance higher than 25×10⁴ Ω·cm. The resulting dispersion isboiled for 5 minutes on an electric heater. After cooling to roomtemperature, the dispersion is replenished with pure water so that thetotal weight is 200±0.1 g. The suspension is measured for electricalconductivity at 18° C. using an electric conductivity meter ("CM-30S"from Toa Dempa Co., Ltd.) The reading is converted into the specificresistance as follows.

Specific resistance (Ω·cm)=1/R×10⁶ where R is the electric conductivity(μS/cm).

                  TABLE 1                                                         ______________________________________                                                                  Rise in                                                                       filtration                                                                              Speciflc                                                            pressure  resistance                                Sample                                                                              Treatment of titanium oxide                                                                       (kPa/4 min)                                                                             (Ω · cm)                   ______________________________________                                        A     Dispersion in water, removal of                                                                   92        7400                                            coarse particles by centrifuge,                                               drying, and crushing of coarse                                                particles by dry crusher                                                B     Dispersion in water, and removal of                                                               128       7400                                            coarse particles by centrifuge                                          C     Dispersion in ethylene glycol, and                                                                135       2800                                            removal of coarse particles by                                                centrifuge                                                              D     Crushing of coarse particles by dry                                                               105       2800                                            crusher (10 kg/h)                                                       E     Crushing of coarse particles by dry                                                               95        2800                                            crusher (5 kg/h)                                                        ______________________________________                                    

Example 1 and Comparative Examples 1, 10, 19, and 28

Each of titanium oxide samples A to E was dispersed into ethylene glycolto give a suspension (slurry), 16 g/100 cm³ in concentration. Apolyester (polyethylene terephthalate) was prepared from ethylene glycoland terephthalic acid by continuous direct polymerization using anapparatus consisting of a first esterification vessel, a secondesterification vessel, a first preliminary polymerizer, a secondpreliminary polymerizer, and a final polymerizer. The slurry was addedcontinuously to the oligomer (with 97% esterification) during itstransfer from the second esterification vessel to the first preliminarypolymerizer. Thus the final polymerization gave the desired polyesterresin composition composed of a polyester resin and titanium oxide.Incidentally, this polyester resin has an intrinsic viscosity of 0.64measured at 25° C. in o-chlorophenol.

The polyester resin composition was tested for rise in filtrationpressure under the following conditions by using "Melt spinning testerCII" (shown in FIG. 1), available from Fuji Filter

Kogyo Co., Ltd.

Measuring temperature: 300° C.

Feeding rate: 5 g/min

Filter: "Dynaloy Filter X5", having a pore size of 7 μm and a filterarea of 4.52 cm². Available from Watanabe Giichi Seisakusho Co., Ltd.

Rise in filtration pressure was recorded after filtration for 1 hour.The results are shown in Table 2. The polyester resin composition wasspun into a multifilament yarn (4.17 denier for single filament) at arate of 6000 m/min. The frequencies of filament breakage per ton wererecorded during spinning. The results are shown in Table 3.

Example 2 and Comparative Examples 2, 11, 20, and 29

The desired polyester resin composition was prepared in the same manneras in Example 1 except that polymerization was carried out by using abatch-type apparatus for the steps of esterification and polymerizationand the titanium oxide slurry was added to the second step at itsoutset. It was tested in the same manner as in Example 1. The resultsare shown in Table 3.

Example 3 and Comparative Examples 3, 12, 21, and 30

The desired polyester resin composition was prepared in the same manneras in Example 1 except the titanium oxide slurry was added to thepolyester by using a mixer attached to the final polymerizer such thatthe resulting composition contained as much titanium oxide as shown inTable 2. (The mixer is of twin-screw type turning in the samedirections, "TEM-48BS" from Toshiba Kikai Co., Ltd.) It was tested inthe same manner as in Example 1. The results are shown in Table 3.

Examples 4-9 and Comparative Examples 4-9, 13-18, 21-27, 31-36

The desired polyester composition was prepared by any of the methods inExamples 1 to 3 as shown in Table 2. It was tested in the same manner asin Example 1. The results are shown in Table 3.

It is noted from Tables 1 to 3 that the polyester resin compositionpertaining to the present invention suffers filament breakage merelyinfrequently.

                                      TABLE 2                                     __________________________________________________________________________                 Designation                                                                         Method of                                                                           Amount of                                                         of titanium                                                                         polymer-                                                                            titanium oxide in                                                                      Method of incorporation of titanium                   No.                                                                              oxide ization                                                                             composition (wt %)                                                                     oxide into polyethylene                     __________________________________________________________________________                                      terephthalate                               Example    1 A     Continuous                                                                          2.2      into 92% esterified oligomer via eth-                                         ylene glycol slurry                         Example    2 A     Batchwise                                                                           2.2      Same as Example 1                           Example    3 A     Continuous                                                                          2.2      into molten polymer by mixing after                                           polymerization                              Example    4 A     Continuous                                                                          0.4      Same as Example 1                           Example    5 A     Batchwise                                                                           0.4      Same as Example 2                           Example    6 A     Continuous                                                                          0.4      Same as Example 3                           Example    7 A     Continuous                                                                          5.0      Same as Example 1                           Example    8 A     Batchwise                                                                           5.0      Same as Example 2                           Example    9 A     Continuous                                                                          5.0      Same as Example 3                           Comparative Example                                                                      1 B     Continuous                                                                          2.2      Same as Example 1                           Comparative Example                                                                      2 B     Batchwise                                                                           2.2      Same as Example 2                           Comparative Example                                                                      3 B     Batchwise                                                                           2.2      Same as Example 3                           Comparative Example                                                                      4 B     Continuous                                                                          0.4      Same as Example 1                           Comparative Example                                                                      5 B     Batchwise                                                                           0.4      Same as Example 2                           Comparative Example                                                                      6 B     Continuous                                                                          0.4      Same as Example 3                           Comparative Example                                                                      7 B     Continuous                                                                          5.0      Same as Example 1                           Comparative Example                                                                      8 B     Batchwise                                                                           5.0      Same as Example 2                           Comparative Example                                                                      9 B     Continuous                                                                          5.0      Same as Example 3                           Comparative Example                                                                     10 C     Continuous                                                                          2.2      Same as Example 1                           Comparative Example                                                                     11 C     Batchwise                                                                           2.2      Same as Example 2                           Comparative Example                                                                     12 C     Continuous                                                                          2.2      Same as Example 3                           Comparative Example                                                                     13 C     Continuous                                                                          0.4      Same as Example 1                           Comparative Example                                                                     14 C     Batchwise                                                                           0.4      Same as Example 2                           Comparative Example                                                                     15 C     Continuous                                                                          0.4      Same as Example 3                           Comparative Example                                                                     16 C     Continuous                                                                          5.0      Same as Example 1                           Comparative Example                                                                     17 C     Batchwise                                                                           5.0      Same as Example 2                           Comparative Example                                                                     18 C     Continuous                                                                          5.0      Same as Example 3                           Comparative Example                                                                     19 D     Continuous                                                                          2.2      Same as Example 1                           Comparative Example                                                                     20 D     Batchwise                                                                           2.2      Same as Example 2                           Comparative Example                                                                     21 D     Continuous                                                                          2.2      Same as Example 3                           Comparative Example                                                                     22 D     Continuous                                                                          0.4      Same as Example 1                           Comparative Example                                                                     23 D     Batchwise                                                                           0.4      Same as Example 2                           Comparative Example                                                                     24 D     Continuous                                                                          0.4      Same as Example 3                           Comparative Example                                                                     25 D     Continuous                                                                          5.0      Same as Example 1                           Comparative Example                                                                     26 D     Batchwise                                                                           5.0      Same as Example 2                           Comparative Example                                                                     27 D     Continuous                                                                          5.0      Same as Example 3                           Comparative Example                                                                     28 E     Continuous                                                                          2.2      Same as Example 1                           Comparative Example                                                                     29 E     Batchwise                                                                           2.2      Same as Example 2                           Comparative Example                                                                     30 E     Continuous                                                                          2.2      Same as Example 3                           Comparative Example                                                                     31 E     Continuous                                                                          0.4      Same as Example 1                           Comparative Example                                                                     32 E     Batchwise                                                                           0.4      Same as Example 2                           Comparative Example                                                                     33 E     Continuous                                                                          0.4      Same as Example 3                           Comparative Example                                                                     34 E     Continuous                                                                          5.0      Same as Example 1                           Comparative Example                                                                     35 E     Batchwise                                                                           5.0      Same as Example 2                           Comparative Example                                                                     36 E     Continuous                                                                          5.0      Same as Example 3                           __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                 Designation                                                                         Amount of                                                               of titanium                                                                         titanium oxide in                                                                      Rise in filtration                                                                    Frequencies of filament                             No.                                                                              oxide composition (wt %)                                                                     pressure (MPa/h)                                                                      breakage per ton                          __________________________________________________________________________    Example    1 A     2.2      0.54    0.3                                       Example    2 A     2.2      0.60    0.3                                       Example    3 A     2.2      0.62    0.4                                       Example    4 A     0.4      0.19    0.0                                       Example    5 A     0.4      0.22    0.1                                       Example    6 A     0.4      0.26    0.1                                       Example    7 A     5.0      1.02    0.5                                       Example    8 A     5.0      1.12    0.5                                       Example    9 A     5.0      1.19    0.5                                       Comparative Example                                                                      1 B     2.2      0.88    1.5                                       Comparative Example                                                                      2 B     2.2      0.92    1.6                                       Comparative Example                                                                      3 B     2.2      1.00    2.5                                       Comparative Example                                                                      4 B     0.4      0.45    0.9                                       Comparative Example                                                                      5 B     0.4      0.52    1.0                                       Comparative Example                                                                      6 B     0.4      0.53    1.0                                       Comparative Example                                                                      7 B     5.0      1.52    2.5                                       Comparative Example                                                                      8 B     5.0      1.62    3.5                                       Comparative Example                                                                      9 B     5.0      1.87    3.7                                       Comparative Example                                                                     10 C     2.2      0.95    2.0                                       Comparative Example                                                                     11 C     2.2      0.99    2.2                                       Comparative Example                                                                     12 C     2.2      1.03    3.5                                       Comparative Example                                                                     13 C     0.4      0.56    1.2                                       Comparative Example                                                                     14 C     0.4      0.57    1.4                                       Comparative Example                                                                     15 C     0.4      0.62    1.5                                       Comparative Example                                                                     16 C     5.0      1.66    3.5                                       Comparative Example                                                                     17 C     5.0      1.80    3.8                                       Comparative Example                                                                     18 C     5.0      1.89    3.9                                       Comparative Example                                                                     19 D     2.2      0.66    1.2                                       Comparative Example                                                                     20 D     2.2      0.69    1.5                                       Comparative Example                                                                     21 D     2.2      0.71    1.6                                       Comparative Example                                                                     22 D     0.4      0.30    0.8                                       Comparative Example                                                                     23 D     0.4      0.39    0.9                                       Comparative Example                                                                     24 D     0.4      0.40    1.0                                       Comparative Example                                                                     25 D     5.0      1.25    2.5                                       Comparative Example                                                                     26 D     5.0      1.26    2.6                                       Comparative Example                                                                     27 D     5.0      1.30    2.9                                       Comparative Example                                                                     28 E     2.2      0.95    2.4                                       Comparative Example                                                                     29 E     2.2      1.02    2.6                                       Comparative Example                                                                     30 E     2.2      1.13    2.8                                       Comparative Example                                                                     31 E     0.4      0.59    1.3                                       Comparative Example                                                                     32 E     0.4      0.64    1.5                                       Comparative Example                                                                     33 E     0.4      0.65    1.7                                       Comparative Example                                                                     34 E     5.0      1.63    3.6                                       Comparative Example                                                                     35 E     5.0      1.75    3.8                                       Comparative Example                                                                     36 E     5.0      1.97    4.0                                       __________________________________________________________________________

Exploitation in Industry

The present invention greatly contributes to the synthetic fiberindustry because the specific titanium oxide produced by the improvedprocess makes the thermoplastic resin composition incorporated therewithless subject to filament breakage during spinning.

We claim:
 1. Centrifuged and dry crushed titanium oxide particlescharacterized by their property that when the particles disperse intoethylene glycol to give a 13% suspension which passes through a filterpaper with a pore size of 6 μm at a rate of 1.73 cm³ /min·cm² such thata rise in a filtration pressure after filtration for 4 minutes does notexceed 100 kPa and that the particles have a specific resistance higherthan 7000 Ω·cm.
 2. A thermoplastic resin composition which comprises athermoplastic resin and the titanium oxide defined in claim
 1. 3. Athermoplastic resin composition which comprises a polyester resin andthe titanium oxide defined in claim
 1. 4. A polyester resin compositionwhich is composed of a polyester resin and a multiplicity of centrifugedand dry crushed titanium oxide particles, and is characterized by theproperty that said resin composition passes through a filtrationpressure tester under the following conditions such that the rise infiltration pressure after filtration for 1 hour satisfies the equation(I) below:Measuring temperature: 300° C. Rate of filtration: 1.11g/min·cm² Pore size of filter: 7 μm

    P≦0.2C+0.2                                          (I)

where P is the rise in filtration pressure (MPa) and C is the content(wt %) of titanium oxide in the composition, provided that 0.3≦C≦15. 5.A process for producing a polyester resin composition composed of apolyester resin and titanium oxide, said process comprising adding asuspension in ethylene glycol of the titanium oxide defined in claim 1in the course of polymerization for polyester resin.
 6. A process forproducing a polyester resin composition composed of a polyester resinand titanium oxide, said process comprising incorporating, by using amixer, the titanium oxide defined in claim 1 into a polyester resinafter the polymerization for the polyester resin is substantiallycomplete.
 7. A process for producing titanium oxide which comprises thesteps of dispersing raw titanium oxide into a liquid, clearing theresulting titanium oxide dispersion of selected titanium oxide particlesby centrifuging and dry crushing, freeing the titanium oxide dispersionof liquid by drying, and causing the titanium oxide obtained in theprevious step to impinge upon an object by the aid of a gas stream.
 8. Aprocess as defined in claim 7 which gives rise to titanium oxidecharacterized by its property that it disperses into ethylene glycol togive a 13 wt % suspension which passes through a filter paper with apore size of 6/μm at a rate of 1.73 cm³ /min ·cm² such that a rise in afiltration pressure after filtration for 4 minutes does not exceed 100kPa and that the particles have a specific resistance higher than 7000Ω·cm.
 9. The titanium oxide particles of claim 1, produced by a processcomprising the steps of dispersing raw titanium oxide into a liquid,clearing the resulting titanium oxide dispersion of selected titaniumoxide particles by centrifuging and dry crushing, removing the liquidfrom the dispersion, and crushing the titanium oxide left after removingthe liquid.
 10. The thermoplastic resin composition of claim 3, whereinsaid composition comprises from about 0.4 percent to about 5 percent byweight of said titanium oxide particles.
 11. The thermoplastic resincomposition of claim 2, wherein said composition comprises from about0.3 percent to about 15 percent by weight of said titanium oxideparticles.
 12. The titanium oxide of claim 9, wherein said removingcomprises evaporating.
 13. The titanium oxide of claim 9, wherein saidcrushing comprises causing said titanium oxide to impinge upon an objectby the aid of a gas stream.
 14. The polyester resin of claim 4, furthercharacterized by its property that a suspension of about 10 percent byweight of said titanium oxide in pure water has an electricalresistivity at 18° C. of at least 7000 Ω·cm.